1. Field of the Invention
The present invention relates to a bush that is incorporated into a connecting portion of a vehicle suspension. More specifically, the present invention relates to a technique by which the setting of a spring constant can be easily changed.
2. Description of the Related Art
A torsion beam type suspension is one of rear-wheel suspensions used for a front-wheel drive vehicle, in which right and left trailing arms are connected with each other by a torsion beam (see, e.g., JP-A-2001-113925). Although the torsion beam type suspension is relatively simple and compact, it is advantageous in that a comfortable driving and stable turning can be obtained. In the torsion beam type suspension, a bush (compliance bush) is attached to a front end portion of each trailing arm in order to prevent vibration caused by a road surface from being transmitted to a vehicle body (see, e.g., JP-A-2003-343625). As shown in FIG. 10, a bush 11 includes a metallic inner cylinder 12, a metallic outer cylinder 13, and a cylindrical elastic member 14 interposed between the inner cylinder 12 and the outer cylinder 13. The bush 11 is press-fitted into a holding cylinder 9 formed at a front end portion of a trailing arm 2. For a purpose of positioning at the time of press-fitting, a flange 21 that comes into contact with an end face of the holding cylinder 9 is provided on the outer cylinder 13.
When a vehicle turns, a strong force in a lateral direction is applied to the torsion beam type suspension from wheels. Therefore, in order to enhance maneuvering stability of the vehicle, it is necessary to suppress a lateral displacement of the trailing arm 2. Thus, in the bush 11 shown in FIG. 10, an elastic brim 22 is formed so as to cover the flange 21 and to extend from the cylindrical elastic member 14. This elastic brim 22 comes into pressure contact with an inner wall of a vehicle side bracket 15 when the trailing arm 2 moves in the lateral direction. In the trailing arm 2 shown in FIG. 10, the axial center I of the holding cylinder 9 is inclined by a predetermined angle α with respect to the oscillating axis L of the trailing arm 2. The reference numerals 16 and 17 shown in FIG. 10 are a bolt and a nut for attaching the bush 11 to the vehicle side bracket 15.
In the bush 11 shown in FIG. 10, thick portions 22a, 22b are respectively formed in a front end portion and a rear end portion of the elastic brim 22, substantially at the center in the vertical direction. Due to such structure, as shown in FIG. 11, in the case where the trailing arm 2 is moved in the lateral direction, the thick portions 22a, 22b of the elastic brim 22 come into elastic contact with the vehicle side bracket 15. Therefore, a displacement in the lateral direction of the trailing arm 2 can be suppressed and the maneuvering stability can be enhanced. As shown in FIG. 12, even in case where the holding cylinder 9 of the trailing arm 2 is rotated when driving on a bad road, a gap “a” exists between the elastic brim 22 and the vehicle side bracket 15, that is, the elastic brim 22 and the vehicle side bracket 15 are not in contact with each other. Therefore, the vehicle is comfortable to drive, and the durability of the elastic brim 22 can be ensured. Further, the generation of noise can be prevented.
However, in the bush 11 described above, when the trailing arm 2 moves in the lateral direction, the thick portions 22a, 22b, which come into elastic contact with the vehicle side bracket 15, are compressed and deformed (or crushed). At this time, since the thickness of the thick portions 22a, 22b is large, an amount of deformation becomes large. Accordingly, an amount of the displacement in the lateral direction of the trailing arm 2 is increased, and it is impossible to enhance the maneuvering stability. Further, in the bush 11, each time the vehicle turns, the thick portions 22a, 22b are greatly compressed and deformed. Therefore, the durability of the elastic brim 22, that is, the durability of the bush 11 is deteriorated. Since the bush 11 is held by being press-fitted into the holding cylinder portion 9, when a permanent set in fatigue is caused by using the bush 11 for a long period of time, there is a possibility that the bush 11 is drawn out from the holding cylinder portion 9.